Protein synthesis is initiated with a methionine residue in eukaryotic cells, or a formylated methionine in prokaryotes, mitochondria and chloroplasts. For a large subset of proteins, the initiator methionine is cotranslationally removed prior to further post-translational modification. The proteolytic removal of N-terminal methionine is catalyzed by a family of enzymes known as methionine aminopeptidases (MetAPs). The functions of these enzymes are evolutionally conserved and essential, as demonstrated by the lethal phenotype of the map null mutant in bacteria. Although only one MetAP gene is present in the genome of most, but not all, prokaryotes, at least two types of MetAPs, type I and type II, are known in eukaryotic cells. In budding yeast Saccharomyces cerevisiae, deletion of either ScMetAP1 or ScMetAP2 resulted in a slow-growth phenotype compared to the wild type strain, whereas the double mutant is non-viable, indicating the redundant yet essential functions of both types of MetAP (Chang, Y. H., et al. (1992) J. Biol. Chem. 267, 8007-8011; Li, X. & Chang, Y. H. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 12357-12361). In multi-cellular organisms, MetAP2 has been shown to be essential for the proliferation and development of specific tissues (Boxem, M., et al., (2004) FEBS Lett. 576, 245-250; Cutforth, T. & Gaul, U. (1999) Mech. Dev. 82, 23-28).
Human MetAP2 has been identified as the primary target of the fumagillin family of natural products that potently inhibit angiogenesis (Griffith, E. C., et al. (1997) Chem. Biol. 4, 461-471; Sin, N., et al. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 6099-6103). A synthetic analog of fumagillin, TNP-470 with higher potency and lower toxicity, has entered clinical trials for a variety of cancers (Ingber, D., et al. (1990) Nature 348, 555-557; Satchi-Fainaro, R., et al. (2005) Cancer Cell 7, 251-261). Much evidence now exists supporting the notion that HsMetAP2 plays an important role in endothelial cell proliferation and is likely to mediate inhibition of endothelial cells by fumagillin and related analogs (Griffith, E. C., et al. (1997) Chem. Biol. 4, 461-471; Sin, N., et al. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 6099-6103; Yeh, J. R., et al. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10379-10384).
Angiogenesis may be defined as the development of a blood supply to a given area of tissue. The development of a blood supply may be part of normal embryonic development, represent the revascularization of a wound bed, or involve the stimulation of vessel growth by inflammatory or malignant cells. Sometimes angiogenesis is defined as the proliferation of new capillaries from pre-existing blood vessels. New growth of soft tissue requires new vascularization, and the concept of angiogenesis is a key component of tissue growth and in particular, a key point of intervention in pathological tissue growth.
Angiogenesis is a fundamental process necessary for embryonic development, subsequent growth, and tissue repair. Angiogenesis is a prerequisite for the development and differentiation of the vascular tree, as well as for a wide variety of fundamental physiological processes including embryogenesis, somatic growth, tissue and organ repair and regeneration, cyclical growth of the corpus luteum and endometrium, and development and differentiation of the nervous system. In the female reproductive system, angiogenesis occurs in the follicle during its development, in the corpus luteum following ovulation and in the placenta to establish and maintain pregnancy. Angiogenesis additionally occurs as part of the body's repair processes, e.g., in the healing of wounds and fractures.
Both controlled and uncontrolled angiogenesis are thought to proceed in a similar manner. Endothelial cells and pericytes, surrounded by a basement membrane, form capillary blood vessels. Angiogenesis begins with the erosion of the basement membrane by enzymes released by endothelial cells and leukocytes. The endothelial cells, which line the lumen of blood vessels, then protrude through the basement membrane. Angiogenic stimulants induce the endothelial cells to migrate through the eroded basement membrane. The migrating cells form a “sprout” off the parent blood vessel, where the endothelial cells undergo mitosis and proliferate. The endothelial sprouts merge with each other to form capillary loops, creating new blood vessels. Creation of the new microvascular system can initiate or exacerbate disease conditions.
Medical science has recognized that angiogenesis is an important factor in the initiation and/or proliferation of a large number of diverse disease conditions. Under normal physiological conditions, humans and other animals only undergo angiogenesis in very specific, restricted situations. For example, angiogenesis is normally observed in wound healing, fetal and embryonic development, and in the formation of the corpus luteum, endometrium and placenta. The process of angiogenesis has been found to be altered in a number of disease states, and in many instances, the pathological damage associated with the disease is related to uncontrolled angiogenesis. Since it was first put forward over thirty years ago, the hypothesis that angiogenesis is required for tumor growth and metastasis has gained extensive experimental support (Folkman, J. (1971) N. Engl. J. Med. 285, 1182-1186, Hanahan, D. & Folkman, J. (1996) Cell 86, 353-364). For example, angiogenesis is a factor in tumor growth, since a tumor must continuously stimulate growth of new capillary blood vessels in order to grow. Angiogenesis is an essential part of the growth of human solid cancer, and abnormal angiogenesis is associated with other diseases such as rheumatoid arthritis, psoriasis, and diabetic retinopathy (Folkman, J. and Klagsbrun, M., Science 235:442-447, (1987)). In addition to tumor growth and metastasis, angiogenesis has also been implicated in rheumatoid arthritis, diabetic retinopathy and macular degeneration, suggesting that inhibition of angiogenesis may be useful for the treatment of these disorders (Carmeliet, P. (2003) Nat. Med. 9, 653-660).
Angiogenesis, the formation of new blood vessels, has been implicated in the pathogenesis of several important human diseases, including cancer, diabetic retinopathy, and age-related macular degeneration. Inhibition of angiogenesis is emerging as an effective new strategy for the treatment of angiogenesis-dependent diseases. One of the most potent classes of small molecule inhibitors is from the fumagillin family. Fumagillin, its synthetic analogue TNP-470, and ovalicin have been shown to specifically bind to type 2 methionine aminopeptidase (MetAP2). In a mechanism that remains to be completely elucidated, inhibition of MetAP2 by these small molecule inhibitors led to the transcriptional activation of p53, which in turn activates the expression of p21 that inhibits cyclinE•Cdk2, accounting for the cell cycle blockade by these inhibitors. Since the identification of MetAP2 as the target for fumagillin and ovalicin, a number of attempts have been made to find new and reversible inhibitors of this enzyme through either the structural modification of fumagillin or high-throughput screening.
Clearly, the development and progress of many disease conditions can be controlled by controlling the process of angiogenesis, and in particular, through the inhibition of MetAP. There is a need for methods and materials capable of controlling and inhibiting angiogenesis in a reliable manner. It is therefore an object of the invention to provide compounds and pharmaceutical compositions which exhibit activity as inhibitors of angiogenesis.